Production of crimped filaments



Oct. 15, 1963 F. REEDER ETAL 3,106,763

PRODUCTION OF CRIMPED FILAMENTS-- Filed July 19, 1961 Fran/r Ree dez 50/5/01 Krzesms/n By fheir af/omeys United States Patent 3,106,763PRUDUCTION 0F CRIMPED FILAMENTS Frank Reader and Boleslaw Krzesiuski,Coventry, England, assignors to Courtaulds Limited, London, England,

a company of Great Britain Filed July 19, 1961, Ser. No. 125,093 Claimspriority, application Great Britain July 27, 1960 13 Claims. (Cl. 28-72)This invention concerns the production of crimped polyacrylonitrilefilaments. By polyacrylonitrile we mean both homopolymers ofacrylonitrile and also copolyrners containing at least 80 percent byweight of acrylonitrile. Such copolymers may be the product ofcopolymerisation with acrylonitrile of such other monomers as styrene,methyl acrylate, itaconic acid, methallyl sulphonic acid and its salts,vinyl acetate and vinyl pyridine. The invention is particularlyapplicable to copolymers containing 90 to 95 percent by weight ofacrylonitrile.

To assist in the conversion of polyacrylonitrile staple fibre to spunyarn, it is usual to crimp the continuous filament tow before it is cutinto staple fibre. The crimping technique most commonly employed forthis purpose involves the use of a stufling box. However, the crimpinserted in the fibre by normal stuffing box techniques may be unstableto subsequent fibre treatment, in particular to boiling, unless specificsteps are taken to impart stability to the crimp.

In order to ensure uniform drying and other early processing offilaments in tow form, it is desirable that some method be provided forimparting a crimp to polyacrylonitrile filaments which have not beensubjected to the first drying after they have been wet-spun. Moreover,if the filaments are crimped at this early stage in their production, itmay be possible to impart a more stable, built-in crimp. However, theuse of a stufling box on filaments still in aquagel form may result inthe filaments being bruised.

Even if it were possible to provide a stuffing-box crimping method whichdid not damage filaments treated while still wet from spinning, it is aninherent disadvantage of stuffing-box methods that the crimp obtained issubstantially two-dimensional. It would be possible to produce filamentshaving better bulk if a crimping method could be invented, which couldbe applied to never-dried polyacrylonitrile filaments to give athree-dimensional crimp. By never-dried filaments we mean filamentswhich have been wet-spun and not subsequently dried.

It is an object of this invention to provide such a process. 0

According to this invention, amethod of producing crimpedpolyacrylonitrile filaments comprises passing never-driedpolyacrylonitrile filaments at an elevated temerature and understretching tension over an edge and ubsequently immersing the stretchedfilaments, under conitions allowing them to shrink, in an aqueous bathat temperature of 70 to 100 C.

The crimped filaments obtained according to the invenshould be driedunder conditions of minimum tenin order to avoid reducing or destroyingthe crimp. erably the tension during drying does not exceed rams/denier.ing from room temperature to the highest temperdepending upon the watercontent of the wet fibres e nature of the drying, at which nosubstantial uration of the filaments occurs. The lower drying tures givethe higher degrees of crimp in terms of of crimps per unit length ofcrimped filament. other hand, since drying is much slower at lower res,for practical reasons the drying is preferied out at 70 to 150 C.

The temperature of drying may be ice The temperature of the filamentswhile they are being stretched over an edge may also vary, withincertain rather narrower limits. The lower limit is determined by thetemperature below which no substantial stretching is possible, which isabout 50 C., while the upper limit is that above which the filaments aredry, viz. about 100 C. A convenient Way of heating the filaments is toimmerse them during stretching in steam or hot or boiling water (i.e.water above about 80 C.), in which case the filaments temperature willbe about 80 to 90 C., depending upon the linear speed of the filamentsthrough the heating zone.

While the filaments are being passed over the edge, they are subjectedto a stretching tension. It is difiicult to collect the never-driedfilaments Without incidentally imparting some stretch, say of the orderof a 2-fold stretch. However, we prefer to stretch the filaments to 8 to14 or more times their original length. Within reasonable limits, thehigher tensions give higher degrees of crimp.

The heating of the filaments to the temperature at which they are to bestretched over an edge may, if desired, be carried out in stages, bypassing the filaments through a bath at a relatively lower temperatureof at least 30 (3.,

by immersing the filaments batchwise in the bath.

for example 60 C., before the hot-stretching operation according to theinvention. In these circumstances, it is also possible to split up thestretching into two stages. For example a 2- or 3-fold stretch in thebath may be followed by a 4-fold stretch over an edge in steam.

The edge may be formed in a body made, for example, of stainless steel,of a ceramic material, or of compressed asbestos. The dimensional natureof the edge is an important factor controlling the crimp produced. Ifthe edge is too blunt, little or no crimp may be obtained. On the otherhand, too sharp an edge may, in combination with a sufficiently hightension or a suificiently small angle between the filaments leadingtowards and away from the edge, result in the filaments, or one or moreof them being severed. In general, the radius of curvature of the edgemay usefully lie in the range of 2 to 40 thousandths of an inch,preferably 4 to 30 thousandths of an inch. The angle of the edge may liebelow 140 degrees of arc and may advantageously lie above 30 degrees. A-degree angle, which is-most readily available, gives whollysatisfactory results. If desired, the member carrying, the edge may bemounted so as to be able to rotate or swing against an appropriateresistance about an axis transversely at right angles to the path of thefilaments, so that irregularities in the filament bundle which mightotherwise foul the edge are able to release themselves (or be releasedby an operator) by turning the edge.

The angle between the filaments approaching the edge and those leavingit is preferably about 60-150 degrees and in general angles between 80degrees and degrees are most useful.

The degree of crimp obtainable by the process according to thisinvention may be improved by subjecting the filaments to coolingimmediately after they have passed over the edge. The cooling may bebrought about by blowing cool air or spraying cool water on to thefilaments or by passing the filaments through a bath of cool water. Theair or water may, for example, be at a temperature of 20 C. or less.A-cooling treatment may thus be combined with a washing of the towinterposed'between the edge-stretching and relaxation stages.

The filaments are next allowed to shrink and crimp in a suitable aqueousbath. The shrinkage may be permitted It is more practicable, however, topass the filaments con- -.tinuously through the bath, while withdrawingthe filaments at a speed sufficiently slower than the feedspeed to allowthe shrinkage to occur. The shrinkage occurring in the bath is usuallymuch less than the stretch originally imparted and may be of the orderof 20 percent, for example.

We have already stated that the temperature of the relaxing bath shouldbe 70 to 100 C. Within this range, the higher degrees of crimp occur atthe higher temperatures, but a disadvantage of higher temperatures whichmust be weighed against their advantage is that they tend to have adelustering eifect on the filaments. Preferably, the bath temperature is80 to 92 C.

The bath in which the filaments are relaxed may contain only water ormay also contain compounds which it is desired to apply to thefilaments, such as finishing agents. The presence of a wetting agent mayprove advantageous. It is therefore possible to combine the relaxingtreatment with other treatments to which the filaments are normallysubjected in the course of manufacture. In particular, by appropriatechoice of bath characteristics and drying conditions, it is possible tocombine the crimping according to this invention with the treatment toimprove fibre properties described in the specification of the abandonedco-pending United States patent application Krzesinski and Hyam, SerialNo. 121,- 354, filed July 3, 1961, and assigned to the same assignee asthe present application.

The denier of the filaments treated is dictated more by the proposedend-use of the filaments or staple fibres than by the requirements ofthe present process. However, filaments of lower denier, say 3 or 6, arein general more easily crimped and give a higher degree of crimp undergiven conditions than do filaments of higher denier, say 9 or 15.

The invention and its advantages are not limited solely to filamentswhich are subsequently to be converted to staple fibre. The productionof a crimp at an early stage in the preparation of the filaments leadsto more easy and uniform processing during, for example, the dryingstage. It is very important that the preparation of filaments or fibresusing heavy tows should result in filaments of uniform properties and itis often in the drying stage that irregularities occur.

The process according to the invention is more simple than stufiing-boxmethods and involves no complicated equipment. The crimp obtained afterdrying is more stable than that produced by most stuffing box methods.Immersion in hot or boiling water for short periods thereafter haslittle adverse effect, while if the crimp is removed by stretching itcan frequently be restored by subjecting the filaments to a furtherassisted relaxation treatment, e.g. immersion in a free-to-shrink statein steam.

In an experiment to test the stability of the crimp, filaments crimpedby the method hereinafter described in Example 1 were immersed inboiling water for minutes and then dried at a temperature in the range80 to 90 C. There was no visible loss of crimp. Another sample of thesame filaments was then stretched by about 12 percent to remove thecrimp and then exposed for one minute to steam at atmospheric pressureand dried at 80 to 90. The crimp in the tow was restored to aconsiderable extent.

The invention will now be further described by means of the followingexamples and by reference to the accompanying drawing, which illustratesthe production of crimped fibres by the method according to the presentinvention. Referring to the drawing, the sequence of operationsillustrated and as used in each of the examples consisted of spinning apolyacrylonitrile dope into a spin bath 1 from which the filaments werewithdrawn over take-up rollers 2 and passed, first through a preheatbath 3 of water at 60 C. and then through a steam box 4. At the end ofthe steam box at which the filaments were withdrawn they passed over asharp-edged guide 5 and thence, over output rollers 6 by which thestretching force was applied, and sprayed with cold Water from a spray7, to a number of washing troughs 8 of water at room temperature. Thewashed filaments were then introduced by a pair of nip rollers 9 intothe relaxing bath 11, from which they were taken by a second pair of niprollers 10 to be collected and subsequently dried. In Examples 1-4,batch drying was employed; in Examples 5-7, the filaments were driedcontinuously in fcstoons.

The dope in each case comprised a polymer containing acrylonitrile andmethyl acrylate residues in the weight proportion-s of 94:6 dissolved ina sodium thiocyanate solution of about 51. percent concentration byweight, the polymer concentration being 12.2 percent by weight. Thespinning bath was a 10 percent by weight solution of sodium thiocyanate.

In Examples 1-4, the edge used was of compressed asbestos and had anangle of 120 degrees and a radius of curvature of 7 thousandths of aninch. The two yarn paths formed an angle of 122 degrees.

upon which they were Example 1 The dope, containing polymer of intrinsicviscosity about 1.5, was spun through a jet having 200 holes of 3thousandths of an inch each and the filaments were withdrawn from thebath at 2.5 metres/min. After preheating and stretching over the edge,the filaments were passed at 20 metres/min. into the first wash trough,the overall stretch therefore being 8 X.

The temperature of the relaxation bath was 90 C. and the shrinkageoccurring therein, compensated by running the withdrawing rolls moreslowly than the feed rolls, was about 20 percent. The time of immersionwas 20 seconds.

The 200/3 den. tow obtained after drying at to C. had an attractive,bulky, wool-like appearance. The individual filaments possessed a mainlyhelical crimp of varying amplitude and of frequency varying between 5and 8 crimps per inch.

Example 2 The dope employed in Example 1 was spun under identicalconditions and the filaments were taken up at 2.5 metres/min. Afterpreheating, the tow was given an 8-fold stretch over the edge and thenwashed.

By immersion for 60 seconds in an aqueous bath at 0., followed by dryingat 80 to 90 C., a tow was obtained in which the attractive, bulkfilaments had a helical crimp varying between 14 and 25 crimps pe inch.

Example 3 The conditions were similar to Example 2, b take-up speed was1.9 metres/min, giving an stretch of 10.5 before the stretched tow wasco at 20 metres/min.

The relaxing treatment consisted of immersio seconds in a bath at 90 C.,and following dry to 90 C. a tow of filaments having 6 to 12 inch wasobtained.

Example 4 Under spinning conditions otherwise sin of the preceding threeexamples, the dope to give a 200/3 den. tow, which was ta. metres/min.The stretch was again 10.5

By immersion for 60 seconds in we of attractive wool-like filaments was0 ments had a helical crimp varying 4 to 9 per inch.

Under spinning conditions s' in Examples 1-4, a 600-denier t was takenup at 2.5 metres/min. a stainless steel edge of 90 deg ture of 13thousandths of an K at the edge made an angle of 92 degrees with theyarn leaving the edge. The following table gives the relaxation anddrying conditions in three separate runs and the crimp results obtained.

Relaxation D 1m rying r ps temp. inch Temp. Time 0.)

( 0.) (seconds) Example 6 Relaxation Drying Orimps/ temp. inch Tern Time0.)

( 0. (seconds) Example 7 Using the spinning and stretch conditions ofExample 6 but a different jet, an 1800-denier tow of 9-denier filamentswas stretched 8-fold over the same 90-degree stainless steel edge. Thefollowing table gives relaxation and drying conditions and results.

Relaxation Drying Crlmps/ temp. inch Temp. Time 0.)

( 0.) (seconds) Whatwe claim is:

1. A method of producing crimped polyacrylonitrile filaments comprisingpassing aquagel polyacrylonitrile filaments at an elevated temperatureand under stretching tension over an edge and subsequently immersing thestretched filaments, under conditions allowing them to shrink, in anaqueous bath at a temperature of 70 to 100 C.

2. A method as claimed in claim 1, in which the temperature of thefilaments during stretching is 50 to 100 C.

3. A method of producing crimped polyacrylonitrile filaments comprisingimmersing aquagel polyacrylonitrile filaments in an aqueous medium whichis at at least 80 C. and simultaneously stretching the filaments between8-fold and 14-fold over an edge, and subsequently immersing thefilaments, under conditions allowing them to shrink, in an aqueous bathwhich is at 70 to 100 C. I

6 4. A method of producing crimped polyacrylonitrile filaments,comprising immersing aquagel polyacrylonitrile laments in water at atleast 30 C. and simultaneously stretching the filaments, immersing thefilaments in an aqueous medium at at least C. and simultaneouslystretching the filaments further over an edge, the total stretch beingsuflicient to i-ncrease the length of the filaments to between 8 and 14times their original length and thereafter immersing the filaments,under conditions allowing shrinkage, in an aqueous bath which is at 70to C.

5. A method of producing crimped polyacrylonitrile filaments comprisingstretching the aquagel filaments, while immersed in an aqueous mediumselected from steam and water at at least 80 C., to between 8 and '14times their original length, over an edge which encloses an angle of 30to degrees and which has a radius of curvature between 2 and 40thousandths of an inch, and subsequently immersing the filaments, underconditions allowing shrinkage, in an aqueous bath having a temperatureof 70 to 100 C.

6. A method as claimed in claim 5, in which the radius of curvature ofthe edge is from 4 to 30 thousandths of an inch.

7. A method as claimed in claim 6, in which the filaments enclose anangle at the edge of between 60 and degrees.

8. A method of producing crimped polyacrylonitrile filaments, comprisingstretching the aquagel filaments, while immersed in an aqueous mediumselected from steam and water at at least 80 C., to between 8 and 14times their original length, over an edge which has a radius ofcurvature of 4 to 30 thousandths of an inch, feeding the filamentscontinuously into an aqueous bath having a temperature of 70 to 100 C.,withdrawing the filaments continuously from the bath at a slower rate,and drying the filaments at a temperature of 70 to 150 C.

9. A method as claimed in claim 8, in which the aqueous bath is at 80 to92 C.

10. A method as claimed in claim 8, in which the filaments are cooledbetween the stretching and the immersion in the aqueous bath.

11. A method as claimed in claim 10, in which the filaments are cooledby contact with a fluid medium below 20 C.

12. A method of producing crimped polyacrylonitrile filaments,comprising immersing the aquagel filaments in steam, simultaneouslystretching the filaments to between 8 and 14 times their original lengthover an edge which has a radius of curvature of 4 to 30 thousandths ofan inch, feeding the filaments continuously into an aqueous bath whichis at 70 to 100 C., withdrawing the filaments continuously from the bathat a slower rate, and drying the filaments, under a tension notexceeding 10 milligrams/denier, at a temperature of 70 to 150 C.

13. A method as claimed in claim .12, in which the aqueous bath containsa wetting agent.

FOREIGN PATENTS Great Britain Oct. 8, 1958

1. A METHOD OF PRODUCING CRIMPED POLYACRYLONITRILE FILAMENTS COMPRISINGPASSING AQUAGEL POLYACRYLONITRILE FILAMENTS AT AN ELEVATED TEMPERATUREAND UNDER STRETCHING TENSION OVER AN EDGE AND SUBSEQUENTLY IMMERSING THESTRECTCHED FILAMENTS, UNDER CONDITIONS ALLOWING THEM TO SHRINK, IN ANAQUEOUS BATH AT A TEMPERATURE OF 70* TO 100*C.